Solar collectors gather direct and limited ambient sunlight and direct it toward a target area. Active solar collector systems employ a mechanism for tracking the sun's trajectory across the sky to maximize the amount of sunlight collected. Active systems may be highly efficient solar collectors, however the required tracking mechanisms add complexity and expense to the system. By contrast, passive solar collector systems employ a fixed reflector system to direct light toward a target area. Passive systems are relatively less complex and less expensive, however passive systems are generally less efficient than active systems.
Daylighting systems are a particular type of solar collector which may be used to provide illumination for the interior of a building by directing daylight into the building. Daylight, as used in connection with the present invention, includes all forms of sunlight whether direct or ambient. Because of cost constraints, most daylighting systems are passive systems which employ fixed reflectors and/or refractors to direct daylight through an aperture into a building.
Ignoring, for the moment, the teachings of Copernicus, it is well known that the trajectory of the sun's path across the sky changes during the course of a year. For the purposes of the present invention, the solar altitude angle (.beta.) shall be the angle between a straight line extending from an object on Earth to the sun (considered a point source) and the horizon. The solar azimuth angle (.alpha.) is the angle between a straight line extending from the object to the sun and an imaginary north-south plane extending through the object. As a matter of convention, east is considered negative while west is considered positive. Solar azimuth and altitude angles vary widely in different geographic locations and during different seasons of the calendar year. However, most solar collectors are designed to accommodate only limited movement of the sun.
The simplest daylighting systems include windows and skylights. Skylights positioned on a flat roof surface are efficient solar collectors when the sun is disposed at high solar altitude angles, however their efficiency drops rapidly as the solar altitude angle drops because the effective aperture through which sun may pass decreases with the solar altitude. Vertical windows present an analogous problem. To compensate for this effect, daylighting systems typically incorporate reflectors or refractors designed to direct low solar altitude angle sunlight into the building.